1. Field of the Invention
The present invention relates to an alignment method for disposing an object to be inspected in position on a defect inspection apparatus in defect inspection of a semiconductor device such as a DRAM or a microcomputer, or a display device such as a TFT or a PDP. The invention also relates to a semiconductor device having a predetermined alignment mark.
2. Background of the Invention
The defect inspection is carried out halfway through a manufacturing process of the semiconductor device or the display device. The defect inspection apparatus requires accurate positioning of a testing chip that may be any part of a testing object, such as a semiconductor device, on a stage. Thus, an alignment mark for alignment is attached to the chip.
FIG. 28 is a plan view showing the component of a chip 200 on the testing object. A rectangular alignment mark 100 is attached to the chip. In order to ensure exact alignment motion on the chip 200, an operator specifies a predetermined alignment point on the alignment mark 100 and teaches the coordinates of the alignment point and alignment mark image to the defect inspection apparatus. FIG. 29 is a view of a teaching screen 300. The alignment mark 100 is displayed thereon. For example, a point of intersection of sides 10a and 10b of the alignment mark 100 is specified as an alignment point AP100, and the image of the alignment mark 100 and the position of the specified alignment point AP100 are taught to and stored in the defect inspection apparatus.
To locate the testing chip 200 in position in the defect inspection apparatus, the defect inspection apparatus searches the chip 200 located on the stage of the apparatus for the same figure as the taught alignment mark 100, using image signal processing technique. Then, the alignment point AP100 is decided on the basis of the discovered figure.
However, automatical searching of the alignment mark by the defect inspection apparatus is getting increasingly difficult due to, for example, an introduction of a CMP (Chemical Mechanical Polishing) method to a planalization technique for a wafer surface. When the automatical searching by the defect inspection apparatus fails, an operator searches for the alignment mark manually and locates the stage in position. FIG. 30 is an illustration of the testing chip for the manual alignment operation. The operator search the chip 200 for the alignment mark 100 within a lens view field 400 of a lens of the defect inspection apparatus, while moving the chip 200 by driving the stage of the defect inspection apparatus. After discovering the alignment mark 100, the operator decides the alignment point AP100 from the discovered alignment mark 100, following the procedure for designating the alignment point AP100. Then, the testing object which includes the chip 200 is moved by driving the stage of the defect inspection apparatus so that the specified alignment point AP100 is superimposed on a center O of a target scope 50 displayed at the lens view field 400. The target scope center O is the landmark of the apparatus detection point (coordination).
FIG. 31 shows that the alignment mark 100 has the indistinct threefold outline. This kind of phenomenon may occur in both cases where the alignment mark 100 is displayed on the teaching screen 300 so that the alignment point etc. is taught to the defect inspection apparatus, and where the alignment mark 100 is displayed at the lens view field 400 in inspection. Thus, aside from the case where one and the same operator conducts an inspection and teach the alignment point location to the defect inspection apparatus, when one operator conducts an inspection and another operator do the teaching, they may decide that a wrong position be the alignment point because of their differences of recognition of the figure outline. This prevents accurate alignment. Such a problem will arise, for example, when one operator teaches the alignment point AP100 to the defect inspection apparatus while another operator decides an alignment point AP101 in inspection. Further, when the point previously taught at the other process is taught as the alignment point, the same problem will arise because of differences of layers to be formed.
FIGS. 32 to 35 sequentially show the alignment method improving accuracy in alignment. With a coarse alignment mark 100 and a fine alignment mark 101 formed on a chip 201, the testing chip is aligned on the basis of the coarse alignment mark 100 in the same way as described above (see FIG. 33). The chip is then aligned on the basis of the fine alignment mark 101 after the lens set at the defect inspection apparatus is changed into a higher-powered one (see FIGS. 34 and 35). However, since the coarse alignment mark 100 and the fine alignment mark 101 are separately formed, an area necessary to form the alignment mark is increased, and accordingly, an element forming area of the chip 201 is reduced.
A first aspect of the present invention is directed to an alignment method comprising steps of: searching for an alignment mark of a testing object; recognizing first and second angles which are previously specified on the basis of the outline of a figure forming the alignment mark, from the discovered alignment mark; and deciding an intersection of a first bisector of the first angle and a second bisector of the second angle to be an alignment point.
Preferably, according to a second aspect of the present invention, in the alignment method according to the first aspect, each of the first and second angles is formed by specifying two line segments out of a plurality of line segments and crossing said line segments. The plurality of line segments form the outline.
Preferably, according to a third aspect of the present invention, in the alignment method according to the first aspect, a search for the alignment mark is conducted within a lens view field where a target scope having first and second axes is displayed. The first and second axes are arranged in parallel with the first and second bisectors, respectively.
Preferably, according to a fourth aspect of the present invention, in the alignment method according to the third aspect, the figure is a rhombus in shape, and adjacent two angles out of four angles of the rhombus are specified as the first and second angles.
Preferably, according to a fifth aspect of the present invention, in the alignment method according to the fourth aspect, obtaining an intersection of the first and second bisectors is equivalent to obtaining an intersection of two diagonals of the rhombus.
Preferably, according to a sixth aspect of the present invention, in the alignment method according to the third aspect, the alignment mark is a pattern formed on the testing object.
Preferably, according to a seventh aspect of the present invention, in the alignment method according to the sixth aspect, the pattern is a rectangle in shape, and two adjacent angles out of four angles of the rectangle are specified as the first and second angles.
Preferably, according to an eighth aspect of the present invention, in the alignment method according to the first aspect, the alignment mark includes a coarse alignment mark and a fine alignment mark. The alignment method comprises steps of: aligning the testing object on the basis of the coarse alignment mark, using a low-powered lens; and aligning the testing object on the basis of the fine alignment mark after changing the first low-powered lens into a high-powered lens. The fine alignment mark is formed in the coarse alignment mark.
Preferably, according to a ninth aspect of the present invention, in the alignment method according to the first aspect, the alignment mark consists of a plurality of figures.
Preferably, according to a tenth aspect of the present invention, in the alignment method according to the first aspect, the alignment mark is formed in a dicing line.
An eleventh aspect of the present invention is directed to a semiconductor device comprising: an alignment mark wherein an intersection of respective bisectors of first and second angles which is specified on the basis of the outline of a figure forming the alignment mark, is decided to be an alignment point.
Preferably, according to a twelfth aspect of the present invention, in the semiconductor device according to the eleventh aspect, the figure is a rhombus in shape, and adjacent two angles out of four angles of the rhombus are specified as the first and second angles.
According to the first aspect of the present invention, the intersection of the first and second bisectors is decided to be the alignment point, even if the outline of the discovered alignment mark is indistinct. This allows the operators to decide a constant alignment point irrespective of their differences of outline recognition.
Further, according to the second aspect of the present invention, even if the outline of the alignment mark is indistinct and the angles of the figure forming the alignment mark are round in observation, two angles can be appropriately specified to obtain bisectors.
Further, according to the third aspect of the present invention, the first and second axes of the target scope are arranged in parallel with the first and second bisectors, respectively. Thus, the intersection of the first and second axes of the target scope can be decided to be the alignment point. This eliminates the necessity of obtaining the bisectors of the first and second angles, thereby facilitating the decision of the alignment point.
Further, according to the fourth aspect of the present invention, since the figure forming the alignment mark is a rhombus in shape, the first and second bisectors are orthogonal to each other. Thus, the alignment point can be decided by using the conventional crisscross target scope.
Further, according to the fifth aspect of the present invention, the intersection of the diagonals of the rhombus is decided to be the alignment point. This facilitates the decision of the alignment point, in comparison with the case where the intersection of the respective bisectors of the specified first and second angles is decided to be the alignment point.
Further, according to the sixth aspect of the present invention, since the pattern formed on the testing object is used as the alignment mark, there is no necessity to provide an area to form the alignment mark in the testing object.
Further, according to the seventh aspect of the present invention, the rectangular patterns that are generally formed in large numbers in the testing object are used as the alignment mark. Besides, the first and second bisectors are orthogonal to each other. Thus, the alignment point can be easily decided by using the conventional crisscross target scope that is tilted 45 degrees from the vertical axis in the lens view field.
Further, according to the eight aspect of the present invention, the fine alignment mark is formed in the coarse alignment mark. This reduces the area necessary to form the alignment mark, as compared with the conventional case where the coarse alignment mark and the fine alignment mark are separately formed in the testing object.
Further, according to the ninth aspect of the present invention, since the area of the figure can be reduced, the risk that the alignment mark may come off during the process can be reduced accordingly.
Further, according to the tenth aspect of the present invention, since the alignment mark is provided in the dicing line, there is no necessity to provide a region to form the alignment mark in the testing object. This eliminates the necessity of reducing the area of the element-forming region in the testing object.
Further, according to the eleventh aspect of the present invention, the intersection of the respective bisectors of the first and second angles is decided to be the alignment point, even if the outline of the alignment mark is indistinct. This allows the operators to decide a constant alignment point, irrespective of their differences of outline recognition.
Further, according to the twelfth aspect of the present invention, since the figure forming the alignment mark is a rhombus in shape, the first and second bisectors are orthogonal to each other. Thus, the alignment point can be decided by using the conventional crisscross target scope.
An object of the present invention is to achieve the alignment method which allows operators to decide a constant alignment point irrespective of their differences of outline recognition, even if the alignment mark displayed on the teaching screen or at the lens view field, has the indistinct outline. The method requires only a small area to form the alignment mark, while achieving accurate alignment, using the coarse alignment mark and the fine alignment mark.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.